"We could not contain our enthusiasm; with one accord we all took off our hats and yelled with all our might." Thus one member of an 1869 expedition reacted to an eruption of Great Fountain Geyser, seen brewing here around trees killed by heat and minerals. The display takes place in Yellowstone's Lower Geyser Basin every 8 to 12 hours. For two million years a plume of magma deep underground has been creating the geysers and stoking their fires.